This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from an application entitled, Method For Charging A Subscriber For A Communication Service According To Time In A Telecommunication Switching System, filed earlier in the Korean Industrial Property Office on Nov. 14, 1999, and there duly assigned Ser. No. 99-48948. 
1. Field of the Invention
The present invention relates to a method for charging a subscriber in a telecommunication switching system for the communication service used by the subscriber, and more particularly, to a technique for correctly computing the call service in the switching system.
2. Description of the related art
When a communication service company charges a subscriber for the communication service they provide to their subscribers, it is very important to correctly compute the actual call time used for the communication service since it forms a basis for charging the subscriber. The computation of such call time is usually performed using a clock system provided in the communication switching system. When the clock system does not agree with real time, the clock system can be adjusted manually to the correct time by an operator, or automatically as occasion demands. For example, when the real time is changed due to the daylight savings time, the clock system should be adjusted to reflect such change. However, if the adjustment is made in the middle of call service when the subscriber is connected to the exchange system, the actual call time used by the subscriber can be measured without compensating for the time change when computing the service charge. As a result, a subscriber can experience over or under charge for the same call service.
It is therefore an object of the present invention to provide an improved computing technique for the communication switching system.
It is another object of the present invention to provide a method for correctly charging a subscriber in a communication switching system for the call service even when the present reference time of the clock system is modified during the call service.
According to one aspect of the present invention, a communication switching system includes a first time counter for registering the starting time of a call service, the first time counter changing the present reference time in response to a command signal during the call service, a second time counter for registering the beginning and the ending time of the call service used by a subscriber, the second time counter being not responsive to the command signal to change the present reference time, and a main processor for calculating the call charge based on the time difference between the beginning time and the ending time registered in the second time counter and the starting reference time registered in the first time counter, so that a subscriber is charged correctly despite the change in the clock system during the call service.
According to another aspect of the present invention, a method for charging a subscriber in a communication switching system for a call service which includes a first and a second time counters, the method comprising the steps of registering the starting time of the call service in the first time counter, registering a duration of the call service in the second time counter, and computing a call charge for the call service based on the starting time registered in the first time counter and the duration of the call service registered in the second counter.